Current TV/Video backlighting systems come in various types.
Edge Lit Backlighting Systems
Current LED display panels require that light be directed through the edge lit panel, reflected off of the back surface of the panel and emitted out of the front surface of the panel. The LCD panel itself consists of a matrix of very small, referred to as pixel, openings also referred to as LCD gates. When a gate is switched open, light passes through until the gate is switched off. In color displays, each pixel is composed of three sub pixels which are Red, Blue, and Green. When all three sub pixels are switched on, the three colors appear to be emitted from the same point and the eye sees white light. When the sub pixels are switched on and off for various time periods the light emitted from the three sub pixels appears as various colors.
Edge lit back light systems are formed of one or more light guides, also called light pipes, and various other plastic sheets or films and air gaps to further direct the light from the light guide(s) and diffuse the light before it is allowed to enter the LCD panel. FIG. 5 shows the various components of an edge lit backlight assembly and its associated LCD panel assembly.
Edge lit display systems are generally thinner and weigh less than direct LED back light systems.
Direct LED Backlighting Systems
Direct LED backlight systems typically have an array of LEDs mounted on a printed circuit board (PCB) with a reflective sheet or layer residing on the top side of the PCB through which the LEDs protrude.
Because of the greater number of LEDs used in a direct LED backlight as opposed to the smaller number of LEDs used in an edge lit backlight, the amount of power used is greater and the amount of heat generated by the LEDs is greater. Direct LED backlight assemblies are also substantially thicker than edge lit LED backlight assemblies.
FIGS. 6 and 7 are depictions of direct LED backlight systems. In FIG. 6, components to the left of the dashed vertical line comprise the direct LED backlight assembly. To support the weight of the direct LED backlight assembly, a rigid sheet metal support 31 is used as a mounting structure. Some direct LED backlights have standoffs 32 between the sheet metal support 31 and PCB 33. Light reflector 34 resides in front of PCB 33 to reflect any stray light emitted by LEDs 35. FIG. 7 depicts the reflector sheet 34 with holes 36 to allow LEDs 35 to protrude through reflector 34. A diffuser 25 resides in front of LEDs 35 to further blend and eliminate bands of light from the array of LEDs 35.